1. Field of the Invention
The present invention relates to an optical fiber array, and particularly to a structure of an end portion of an optical fiber.
2. Description of the Related Art
In recent years, increase in a capacity and a speed of an optical communication network has been facilitated due to a progress in optical fiber communication. With such a trend, an optical fiber array has been used highly frequently as a constituent element which forms an optical splitter which divaricates an optical fiber into a plurality (for example eight) fibers, an optical demultiplexer which separates light according to each wavelength range, and further, an optical switch which converts a direction of light. An optical fiber array has been used as an optical coupling means in optical guided wave path components and optical demultiplexers.
An example of such optical fiber array will be described below while referring to an example of use. An optical guided wave path component is one of components that form an optical transmission body. The optical guided wave path component, as shown in FIG. 13, has a guided wave path substrate 101 and a cover 102 which is disposed on the optical guided wave path substrate 101. Furthermore, a plurality of cores 103 is disposed in a state of being exposed at a predetermined position and at a predetermined interval on a guided wave path substrate terminal portion 104 which is a connecting end surface with a terminal portion of another optical transmission body. An optical fiber array 105 shown in the same FIG. 13 is to be connected to an optical guided wave path component 100 which includes the guided wave path substrate 101. The optical fiber array 105 includes a plurality of optical fibers 106 and a substrate 107, and a V-groove 108 which holds a terminal of the optical fiber 106 is disposed at a predetermined interval in a straight line on the substrate 107. A predetermined number of the plurality of optical fibers 106 is disposed in a row in the V-groove 108, and stuck by an adhesive and fixed by a cover 109.
The optical guided wave path component 100 and the optical fiber array 105 are connected by matching the optical fiber array 105 and the cores 103 face-to-face, and then by fixing by adhering both terminals, after the alignment is carried out. Moreover, for connecting optical fibers which form an optical transmission body, it is common to use a multi-fiber optical connector.
Moreover, as another example of use of an optical fiber array, a structure of an optical demultiplexer will be described below.
In FIG. 14, there is shown an optical demultiplexer 110 in which, a diffraction grating 114 which separates a wavelength multiplexed signal in multi-spectral channels at a wavelength unit, and focuses on an array of corresponding channel micro mirrors 111 is used. Each of The channel micro mirrors 111 are controllable individually to reflect a spectral channel to a multi-output port 112, and can be rotated continuously. The optical demultiplexer 110 is capable of routing a spectral channel according to a wavelength as a base, and is capable of combining an arbitrary spectral channel at an arbitrary at any multi-output port 112. Furthermore, the optical demultiplexer 110 is provided with a servo control and a spectrum output controlling capability, by which, the optical demultiplexer 110 maintains an efficiency of combining the spectral channels at the multi-output port 112. Such optical demultiplexer 110 is used for structuring a dynamically reconfigurable optical add drop multiplexer (ROADM) of a new type by a wavelength division multiplexing (WDM) optical networking application.
A wavelength multiplexed signal, after being emerged from an input port 113, is incident on the diffraction grating 114, and diffracted. Since an angle of diffraction of diffracted light becomes an angle corresponding to a wavelength by an action of the diffraction grating 114, the diffracted light after passing through a lens 115, is reflected at the channel micro mirror 111, and is combined at the respective multi-output port 112. As an optical guided wave path component which forms the input port 113 and the multi-output port 112, an optical fiber array is used.
In the optical guided wave path component 100 shown in FIG. 13, the core 103 and a cladding which covers the core 103 are stacked on the guided wave path substrate 101. Since each of materials forming the guided wave path substrate 101, the core 103, and the cladding respectively is different, there is a difference in a coefficient of linear expansion. Thereby, warpage is occurred in the optical guided wave path component 100 according to the difference in a coefficient of linear expansion. Therefore, in many cases, a line segment which connects axis centers of the cores 103 in a connecting end surface becomes a predetermined curve. Consequently, as shown in FIG. 13, since it is not possible to connect the core 103 and the optical fiber 106 concentrically by connecting the optical guided wave path component 100 and the optical fiber array 105 in which, the optical fibers 106 are arranged in a row in straight line and fixed, in the V-groove which is formed in a straight line, and a joint loss becomes substantial thereby posing a problem.
Moreover, a resolution of the optical demultiplexer 110 in FIG. 14 is determined by a focal length of the lens 115 and a resolution of the diffraction grating 114 (concretely, an amount of wavelength-angle dispersion of diffraction grating) However, as shown in FIG. 17, in a case of providing a plurality of input ports 113, an optical signal which is incident from the optical fiber 106 of a port arranged in row at a further outer side, is incident on the diffraction grating 114 at angle of inclination. The angle of incidence of the optical signal with respect to the diffraction grating 114 being different for each port for the abovementioned reason (the angle of incidence changes from α1 to α2 in FIG. 17), the angle of diffraction from the diffraction grating 114 also differs for each optical signal of each port (the angle of diffraction changes from β1 to β2 in FIG. 17). Here, α1 and α2 are angles with respect to Y-axis direction in FIG. 17, whereas, β1 and β2 are angles with respect to X-axis direction in FIG. 17. When the angle of diffraction from the diffraction grating 114 changes for each port, a focusing position of diffracted light on the channel micro mirror 111 is shifted for each port. Due to an effect of such shift in the focusing position, an angle of reflection of the diffracted light at the channel micro mirror 111 also differs for each port.
Consequently, when the optical fibers 112 and 113 are arranged in a straight line, due to the abovementioned reason, since it is not possible to connect the diffracted light reflected at the channel micro mirror 111 in a straight line, there occurs loss at the time of combining at the output port 112.
As a means for solving these problems, an optical fiber array having a structure in which, optical fibers in the form of an array are not arranged in a straight line, but can be arranged at arbitrary positions has been proposed. As an example of such optical fiber array, an optical fiber array in which, an optical fiber contact surface of a cover is let to be at a level corresponding to a cladding diameter of the optical fiber has been contrived (for example, refer to Patent Literature 1, Japanese Patent Application Laid-open Publication No. 2002-40284 (pages 5 and 6, FIG. 1).
An optical fiber array described in Japanese Patent Application Laid-open Publication No. 2002-40284 is shown in FIG. 15A and FIG. 15B. In an optical fiber array 122 in FIG. 15A and FIG. 15B, an angle of formation of V-grooves 106 and 107 for an optical fiber arrangement is set to be constant for all V-grooves, and moreover, a depth of the V-grooves 106 and 107 is set to differ vertically. Furthermore, a rectangular groove (recess) 119 and a rectangular projection (protrusion) 120 corresponding to the depth of the V-grooves 106 and 107 are provided on an optical fiber 121 contact surface of a cover 118. Moreover, a tape-type (tape-form) multi-fiber optical fiber bundle overlapped in a direction of thickness is disposed parallel to a horizontal direction.
Moreover, as an example of an optical fiber array used in a multi-port wavelength selector optical switch, an optical fiber array arranged in an arciform manner has been contrived (for example, refer to Patent Literature 2, FIG. 14 of U.S. Pat. No. 7,162,115(FIG. 18 of the present patent specification)). In FIG. 18, an optical fiber array 131 is arranged in an arciform manner by being pinched from an upper side and a lower side by array holding members 130a and 130b having an interval surface ground to be arc shaped. A curve of the arciform arrangement is set such that a loss of an optical signal is propagated obliquely.
Moreover, as an optical fiber array of other form, an optical fiber array which forms a V-groove having a constant angle of formation, and set at an arbitrary depth has been contrived (proposed) (for example, refer to Patent Literature 3, Japanese Patent Application Laid-open Publication No. Hei 09-5576 (pages 2 and 3, FIG. 1).
In FIG. 16, the optical fiber array disclosed in Japanese Patent Application Laid-open Publication No. Hei 09-5576 is shown. In an optical fiber array 123 in FIG. 16, a plurality of V-grooves 125 is arranged in parallel on an upper surface of a substrate 124 at a predetermined fixed interval. V-grooves 125 positioned at both sides of the plurality of V-grooves 125 are formed to have the maximum depth, and the depth of the V-grooves 125 goes on decreasing toward a center of the linear arrangement of the plurality of V-grooves 125. A projection 127 is provided at both sides of a lower surface of a cover 126, and further, a V-groove 128 is provided at an inner side of the projection 127. Closer a position of the V-groove 128 from a center of the cover 126, more is the depth of the V-groove 128. Optical fibers 129 exposed are disposed in the V-groove 125 of the substrate 124 according to the respective order of arrangement, and after applying an adhesive, all the optical fibers 129 are collectively fixed by putting the cover 126.
In this optical fiber array 123, nearer the V-groove 125 to both sides, the depth of the V-groove 125 goes on increasing progressively, and nearer the V-groove 124 to the center, the depth of the V-groove 125 goes on decreasing progressively. Therefore, as a result, a line segment which has connected fiber centers of an end surface of the optical fiber 129 is arranged to be a predetermined curve. Accordingly, the curve which has connected the fiber centers is same as the curve connecting an axis center of an optical path of an end surface of an optical transmission body which is to be connected (for example a curve connecting an axis center of the core 103 of the optical guided wave path component 100), each optical fiber 129 coincides with each optical transmission of a counterpart to which the axis center thereof is to be connected. Consequently, the connection between the optical fiber array and the optical transmission body is improved, and it is possible to reduce a joint loss.